You've probably heard of Thomas Aquinas because he was so influential, but you may not know why. He's known as the "Doctor of the Church" because he's one of the most influential theologians and philosophers, and he had considerable influence on western thought.
Here's a brief summary:
Thomas Aquinas was a profoundly influential thinker from the thirteenth century. As a scholastic, Aquinas sought to understand Christian theology in light of the rediscovery of Aristotle’s works, and he redefined the relationship between revelation and reason, science and theology, and faith and philosophy for the next eight centuries. As a philosopher, Aquinas developed principles of just war and natural law, and outlined an argument for God’s existence from contingency—the intellectual forerunner to the modern Argument from Design.
Here's more on Aquinas' thinking on the complementary nature of faith and reason:
Christianity’s engagement with non-Christian thought proceeds from the Christian belief that reason and faith are complementary, not oppositional. Thomas Aquinas’ synthesis of Aristotle and Christianity is a vital chapter in this engagement. His interaction with the philosophy of Aristotle demonstrates both the harmony of reason and faith and the oneness of truth, which are both central to the Christian intellectual tradition....
Aquinas felt comfortable undertaking such incorporation because, as he said, “All truth is one.” He argued that what we learn from the natural world through science and philosophy, provided it is unquestionably true, can never contradict that which we learn from revelation, that is, directly from God. He compared Scripture and reason to two books, “the book of revelation” and “the book of nature,” which were both “written” by God and consequently compatible. Therefore, though Aquinas was well educated in the Bible and the writings of earlier theologians, he preferred to base his arguments in logic and philosophical reasoning that could appeal even to nonbelievers. He did so confident in his faith that reason and philosophy would confirm and not contradict the revelation of God.